Gauff, the 15-year-old who reached the fourth round at Wimbledon, and the 17-year-old McNally were given a wild card into the tournament.
American teenager Coco Gauff has won her first WTA title with victory in the Washington Open women's doubles.
Gauf made her WTA main draw debut in March at the Miami Open, ousted 44th-ranked Williams in round one at Wimbledon, then dispatched Slovakia's Magdalena Rybarikova and saved two match points in defeating Slovenia's 60th-ranked Polona Hercog before falling to Romania's Halep.
Murray has not played singles since the Australian Open, but said he might return at the ATP Cincinnati Masters starting on August 12. "It taught me a lot about myself and showed I'll fight no matter what", Gauf said. He will face Nick Kyrgios - with whom he played doubles in the tournament - after the Australian beat Norbert Gombos of Slovakia 6-3, 6-3. "It was definitely a big change", Gauf said.
Also, No. 3 Daniil Medvedev edged sixth-seeded Marin Cilic 6-4, 7-6 (7) to set up a semifinal meeting with Peter Gojowczyk, who continued his surprising run by upsetting No. 13 seed Kyle Edmund 6-3, 4-6, 6-3.
Greece's Sakkari rallied from 1-6, 2-5 down to triumph 1-6, 7-6 (7/3), 6-3 as she remained on course to reach the final for a second straight year. Sixth-seeded Marin Cilic topped ninth-seeded Felix Auger-Aliassime 6-3, 6-4 to set up a match against Nick Kyrgios, a 6-2, 7-5 victor over Yoshihito Nishioka.